The present invention relates to metallurgical furnaces. In particular, the invention relates to metallurgical furnaces of the type having a slag door, such as electric arc furnaces used for steelmaking.
Metallurgical furnaces of the type having a slag door are well known. The slag door is typically positioned on the side of the furnace shell with a tunnel area leading from the furnace interior, and an apron extending below the opening on the exterior of the furnace. The slag door is used for periodic tapping of slag by tipping the furnace, but it is also used for many other operations, including charging of additives, sample collecting, temperature measurement, insertion of burners and oxygen lances, and visual inspection of the furnace interior.
In steelmaking operations, unmolten scrap metal tends to accumulate in the tunnel that extends through the furnace wall from the furnace interior to the slag door opening. Slag can also freeze in large quantities in the area of the tunnel and the threshold of the slag door opening. Commonly, operators must regularly try to clean out these areas by means of tractors equipped with long projecting rams, a technique that has limited efficacy and is also potentially dangerous for the operating personnel.
Known closures for slag doors consist essentially of a sliding panel that can be raised or lowered by a mechanical system of pulleys, sprockets, links and roller chains that is powered by hydraulic or air cylinders. Such closure mechanisms are vulnerable to jamming and blockages, and after being in service for some time, they typically provide only partial coverage of the slag door opening.
As a result, ambient air is sucked into the furnace through the slag door which is believed to lead to a number of drawbacks, including:                heat losses due to excessive volumes of exhaust gas;        excessive pollution in the exhaust gases;        higher energy consumption; and        uncontrolled decanting of slag through the slag door.        
It is therefore an object of the present invention to address the disadvantages of known metallurgical furnaces having slag doors, or at least to provide a useful alternative.